I do not need var3 until func15. Is there a way to fix this mistake without having to change all the function calls and headings? var3 needs to be remembered every time I get to func15. I only use var3 in func15 though so I really do not want to have to change all of my function calls and headings. It obviously can't be a local variable or it will be forgotten each time it is called.

It depends on when the correct value for var3 is known and by whom (i.e. which function). If it is known only by func14, there's no point in changing the code. If it is known before the cascade of functions is called you might make it global. Since you have not stated which language you're using let's assume its c. If you declare var3 outside all functions, it will be visible inside each one including func15.
See: https://www.codingunit.com/c-tutorial-functions-and-global-local-variables